This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The transmission matrix for a highly scattering sample is the linear transformation relating the incident complex, monochromatic wavefield to the scattered wavefield in the forward direction. It can be measured by illuminating the sample with a sequence of plane-wave basis states, and rapidly scanning the illumination angle to cover the range determined by the numerical aperture. Once the matrix has been recorded, it may be analyzed to draw inferences about the nature of the scattering in the medium. In particular, it may be used to identify the existence of "open" scattering channels, illumination states corresponding to near-complete transmission of the wavefield. Analysis is performed by examining the distribution of the transmission matrix singular values, and comparing the results to theoretical predictions.